Method of producing fibrous glass building boards and product



17, 1961 J. A. TOMLINSON 3,

METHOD OF PRODUCING FIBROUS GLASS BUILDING BOARDS AND PRODUCT Filed Aug.16, 1957 3 Sheets-Sheet 1 INVENTOR.

JAMES A. TDMLJNSUN.

ATT'YS Oct. 17, 1961 J. A. TOMLINSON 3,004,878

METHOD OF PRODUCING FIBROUS GLASS BUILDING BOARDS AND PRODUCT Filed Aug.16, 1957 3 Sheets-Sheet 2 Q 57 5 \Qw 1 I I u 7 6/ I I5- INVENTOR: 7/ if;f! JAMES.A.TL7MLINS UN.

# -E D {W Oct. 17, 1961 J. A. TOMLINSON METHOD OF PRODUCING FIBROUSGLASS BUILDING BOARDS AND PRODUCT 3 Sheets-Sheet 3 Filed Aug. 16, 1957Eli-E1- INVENTOR: JAMES A. TUMLINEUN.

15 T TY s.

United States Patent 3,004,878 METHOD OF PRODUCING FIBROUS GLASSBUILDING BOARDS AND PRODUCT James A. Tomlinson, Campbell, Calif.,assignor to Owens-Corning Fiberglas Corporation, a corporation ofDelaware Filed Aug. 16, 1957, Ser. No. 678,586 5 Claims. (Cl. 154-453)This invent-ion rel-ates to building boards having fibrous glass as aprincipal constituent, and particularly to such boards used for thesheathing of walls and pitched roofs.

Fibrous building boards, made of processed wood, bagasse, newsprint andother materials, have become increasingly common sheathing materials.Most are porous enough to have insulating value while sufliciently rigidto withstand handling as well as to provide moderate nail-holding power.Because of the low density of the organic fibers they are closelycompacted to give the board weight and sturdiness. Consequently, thevoids or air spaces in such boards account for only ten to thirtypercent of their total volume.

In contrast to organic fiber boards, more than eighty percent of thevolume of compressed fibrous glass boards usually consists of minute airspaces. This makes them more porous and superior as heat insulators.

Sheathing boards are applied in frame construction against the outersides of wall studs or upon the rafters of a pitched roof. The exteriorfinish of the wall is generally wood siding nailed through the sheathingboard to the wall studding but may be shingles secured upon fun-ingstrips or a brick veneer anchored through the sheathing to the studs.The roof may also be variously finished over the sheathing board withwood shingles or slate laid upon lath or furring strips, asphaltshingles or roll roofing.

Building elements, including sheathing boards are, of course, more orless subject to damage from moisture. In spite of the long-held beliefthat rain and fog are the source of water reaching the interior of wallsand roofs, it is now recognized that moisture problems arise mainly fromwithin buildings. The warm air within a dwelling can hold a large amountof water and usually does because of the water vapor released bywashing, cooking, laundering and other household activities. Severalgallons of water may be introduced into the of a small home each dayfrom such sources.

Through adequate ventilation in winter and air movement through openwindows and doors in summer, this water vapor is carried away. If suchan outlet is not provided, the pressure of the warm vapor will force thevapor through walls and ceilings toward attic, wall spaces and theoutside atmosphere where the vapor pressure is lower. Many materialsconsidered impervious to air will thus permit the passage of watervapor. As long as the vapor is free to continue its normal expansiveflow it will not condense, even in severe winter weather, when chilledto the dew point temperature within the wall structure but will continueto move until dispersed in still colder air.

While a general recommendation is to place a vapor seal in the form of asheeting or coating at or adjacent to the warm side of the walls orpitched roofs of dwellings in order to prevent access thereto ofhousehold moisture, in some climates or conditions such a vapor barrieris not advisable, and may also be omitted as an economic measure in manylocalities.

Where the siding or other outer wall covering is vapor tight, eitherbecause of its basic nature or due to an imperv-ions paint coating,water vapor generated within the dwelling and forcing its way throughthe inner layers of 3,004,878 Patented Oct. 17, 1961 the wall structureto the siding is stopped there, and if the temperature of the siding issufficiently lower than that inside of the dwelling, the vapor iscondensed on the inner surface of or within the siding. The resultingdampness, which is likely to remain for a long period, has a rottingeflect upon the wood siding and adjoining studs, and when vaporized byhigher outside temperatures may cause blistering and peeling in theouter coating of paint.

When the siding strips or other outer structural materials are nottightly assembled or venting ports therethrough exist whether or notintentionally provided, the lack of resistance to the movement of watervapor permits the vapor to continue its travel to the outsideatmosphere. As previously stated, this takes place even though the dewor saturation point resides within the wall structure. This exteriordissipation of the water vapor is, of course, most desirable as itprevents the development of dampness within the walls.

Sheathing boards of glass fibers, because of their large content of airspaces is quite readily permeable to Water vapor and allows the watervapor to reach and pass through a vented exterior layer of siding orother material to the atmosphere.

In contrast, a relatively compact organic fiber board sheathing, whileno heavier than a fibrous glass board, has far fewer air spaces or voidsand tends to resist the flow of water vapor. This resistance, coupledwith a lowering of temperature to the dew point within or adjacent tothe sheathing, condenses the vapor, and the resulting water is thenabsorbed and held in the board whether or not the outer wall surface isvented.

This water. retained by the organic fiber board may remain for anindefinite period, the length of which depends upon how soon the outsidetemperature rises and the degree of vapor permeability possessed by theadjacent wall structure, both interiorly and exteriorly of the board.

Meanwhile, because of the high thermal conductivity of water, the heatinsulating value of the area of the board holding water is practicallyeliminated. In addition, the water, due to the resulting swelling of thefibers and their reduced cohesive properties, has a severe weakeningeffeet on the strength of the board. The dampness further promotesrotting and mildew in the board as well as in adjoining materialssusceptible to such damage.

Where the outer layer of the wall constitutes a vapor seal, thisprecipitation and retention of water within the sheathing board isadvantageous as it is inclined to prevent water condensation on theinterior side of the siding or other surfacing materials and to curtailthe draining of water down to the wall footing members.

The prime object of this invention is to provide a fibrous glassbuilding board which has this water holding virtue of organic boards andwhich also is structurally strong, dimensionally stable, readilypermeable to water vapor, and capable of temporarily holding water ofcondensation without losing its capacity as a heat insulator.

A further object of this invention is to provide a sheathing boardcomposed of fibrous glass and organic fibers which contains a highquantity of voids or small air pockets to make the board effective as aheat insulator and to present low resistance to water vapor movement.

Another object of the invention is a sheathing board which willtemporarily store condensed water but is resistant to the weakening orother deteriorating effects of moisture.

An additional object is a fibrous glass sheathing board in which theglass fibers are bound together and whichv has a component of organicfibers dispersed among the glass fibers.

A further object of the invention is to provide a building board ofglass and organic fibrous material which is firmly held together by abinding agent disposed principally between glass fibers and by thefelting properties of tne organic fibers. i

A still further important object of this invention is to provide asheathing board with channels in its exterior face to serve as pathsreaching venting areas in the exterior wall covering and-hence to theoutside atmosphere for water vapor moving outwardly from the interior ofthe dwelling.

An additional object -is to provide a fibrous sheathing board withcompacted portions which increase thenail holding and racking strengthofthe board. 7

Another object is the provisionof methods for producing fibrous glassbuilding boards having characteristics set forth in the precedingobjects.

In view of the outstanding properties of fibrous glass including itsgreat strength, inertness to weathering agents, and high insulatingcharacter it would appear illogical to combine it in a building boardwith wood or other organic fibers which are inferior in those qualities.

The purpose of this invention, however, is achieved by effecting thisunnatural combination of materials in a building board in a mannerwhereby the undesirable attributes of a board compounded entirely oforganic fibers are excluded.

A principal feature of the invention is the utilization of acomparatively low quantity of the organic fibers as compared to thetotal volume of the finished board. For example, one formulawhich'produces a board of the desired high air content involves twoparts by weight of fibrous glass to one part of organic fibers in aboard having an overall density of sixteen pounds per cubic foot.

However, the proportion of glass fibers to organic fibers may varythrough a wide range within the com cept and practice of this invention.Even-a board having six parts by weight of glass fibers to one oforganic fibers possesses the beneficial properties for which theexecution of the invention is intended. Also, a building boardcontaining as much as one part by weight of the organic fibers to one ofglass fibers will have the desired advantageous features, even thoughthe unfavorable characteristics of the organic material will be muchmore in evidence with such an increasein' the proportion of the organicfiber component.

a In the production of a standard fibrous glass board, fine threads orfilaments of molten glass are drawn down from a series of multi-portedbushings by high pressure steam' or air. A downwardly flaring pipesection or spout receives the fibers for-med from each bushing anddirects them into a hood. As many as eighteen bushings may thus feedglass fibers into a common hood. The bushings -may be in a doublerow andthe hood elongated and rectangular in cross section with itslongerdimension in line with the rows'of bushings and with a conveyortraveling across its lower end upon which the fibers accumulate in packform. From the end walls of the hood strong blasts of an atomized bindersolution are driven into the falling fibers, and the binder particlesare adhered to the fibers as the .latter fall and collect upon theconveyor.

In fabricating aboard according to this invention, the organic fibersmaybe introduced by air blowers into the "hood at several points or addedin smaller air streams to eachbushing spout. Either arrangement providesade quate distribution of the organic fibers throughout the final boardproduct.

Contrary'to the quite logical view that the fibers should be added indry form, an important discovery of this invention is that the organicfibers should be wet when introducedinto'the glass fiber forming hood.If dry they absorb and are coated with the glass fiber binder to anextent where they become'praet-ically water repellent instead of waterabsorbent, the latter being the main qual- 4 j ity for which theirpresence is desired. Further, the binder is comparatively expensive andthe amount thus taken up by the organic fiber would seriously add to theproduction cost.

When wet, the organic .fibers are inclined to repel the binder particlesand thus thelatterare more disposed to attach themselves to the glassfibers. Even so, there is an objectionable amount of the binder lo'stwithin the mass of organic "fibers "when the "latter are added in thefiber glass forming hood, and the preferred'procedure of the inventionis'to first produce-a binder-impregnated pack of glass fibers in theregular way utilizing a lesser quantity of binder. Then the pack,uncured or preferably slightly cured, is torn in a reform 'unitintotufts and clumps, and the organic. fibers are mixed with the thusdisintegrated glass fiber mass before it is reassembled and reformedinto a unitary pack or blanket. Additional binder may be added ifdesired during this reforming operation.

The binder introduced into the original glass fiber forming hood, 'withthe above arrangement, is entirely deposited upon the glass fibers andremains quite completely attached to them when the mass is separatedinto tufts and clumps by'the' reform unit. With this effective use, theamount of the binder'may be reduced as much as fifty percent andthe'factory cost of the cured board cut twenty percent or more. i

'If the organic fibers are wet when then added they will not absorbrthe'binder with which they come in contact and -therefore-do not' draw toomuch of the binder away from itsjproper' glass fiber binding function.In a wet condition, theorganic fibers have a much better felting actionand thus-become more completely tied to each other an the; glass fibers.

There are advantages -'in' "having the organicfibers in a less wet formwhen introduced at the reform "station than when added at the glassfiber forming hood, since the newly formedpack may be cured -morereadily with less moisture to be' evaporated in the curingprocess.

Also, the binder diluting eifect of the water of-the organic fibers islessened,- although the diluting action is minimized by apreceding'p'artial cu're of-the binder, advancing it from'its water'soluble'stage. While some additional binder will be taken up by'drierorganic fibers, it is not here too serious an economic'factor and is farless than that incorporatedin the organic fibers when they are injectedinto the glass fib'er forming hood.

Another feature of theinventi'on is a building board with indentededgesor depressed channels running verticallyin its outer "face.Su'ch'more closely compacted edges or. areas are produced by havingdownwardly Jpro jecting ridges or plateaus in the upper compressionmember in the curingoven. The resulting more compacted areas not onlyadd strength and nail-holding power to the boardbut also; providevertical venting paths by which expanding water vapor may reach escapeports in the outer wall surfacing material.

The various methods referred to for producing building boards according,to this invention are described in more detail hereafterin connectionwith the accompanying drawings in which:

FIGURE 1 is a longitudinal, vertical section of a glass wool or fibrousglass web production line adaptedto produce a building board' accordingto this invention;

FIGURE 2 is a similar view of the same equipment but in which theorganic-fibers are introduced into the main glass fiber'forminghoodinstead of into the spouts leading into the hood;

FIGURE 3 is a longitudinal, vertical section of a reforming unit inwhich a fibrous glass 'web impregnated with binder is'torn into smallpieces, and organic fibers are mixed therewith prior t'othereassembly/of the pieces sesame which the pack of fibrous glass andorganic fibers is compressed and set in board form;

FIGURE is a cross section taken on the line 55 of FIGURE 4 showing theshape of the compressing skid plate by which the edges of the board arecompacted to a greater degree than is the center portion of the board;

FIGURE 6 is a perspective view of part of a board produced by the skidplate of FIGURES 4 and 5;

FIGURE 7 is a perspective illustration of a board with a centrallylocated zigzag channel and compacted edges molded under a compressionconveyor flight having complementary projections; and

FIGURE 8 is a perspective section of a wall showing the installation ofa board of the design of that of FIG- URE 7 as a sheathing member.

Referring to the drawings in more detail, the glass and organic fiberpack production line illustrated in FIG- URE 1 includes the forehearth 2of a glass melting tank. Fine streams of glass are discharged fromorifices in bushings 4. The molten threads of glass are drawn downwardlyand attenuated into fibers by the blast of air or steam jets frommanifolds 6. These fibers are preferably between fifteen and fiftyhundred thousandths of an inch in diameter.

Below each bushing is a guiding spout 8. All of the spouts lead into acommon hood 9. In the arrangement illustrated, wet organic fibers,preferably shredded redwood or fir, are blown into each spout 8 from abranch line 11 of a main delivery piping 12. An air blower 14 furnishesthe pressure for driving the air borne wood fibers into the spouts froma feeding bin 15. These fibers may be utilized in the wet state asdischarged by an Asplund defibrator.

From the ends of the hood through spray nozzles 16 a glass fiber binder,preferably a phenol formaldehyde solution extended with twenty percentvinsol, a rosin suspension, is discharged into the falling fibers. Thebinder may be used in suflicient amount to constitute eight and one halfpercent by weight of the final board. The fibers, with the intermixedbinder, collect in a pack upon the foraminous conveyor 18 travellingacross the bottom of hood 9.

A suction chamber 19 below the conveyor assists the gathering of thefibers upon the conveyor by drawing air downwardly therethrough. Thefibrous pack or web 21 thus formed mayhave a width of four feet and athickness of four to six inches, the latter being governed by the speedof the conveyor and the fiber production rate.

The pack is carried by conveyor 18 to a second conveyor 23 upon which itis compressed to the desired ultimate thickness of one half or threequarters of an inch by an upper conveyor flight 24, or alternately by astationary skid plate. While the pack is under compression the binder isset by the application of curing heat in the oven 25.

After the permanently compacted pack has passed through oven 25, it iscut and trimmed according to the dimensions desired in the finalbuilding board product. With the proportion of glass fibers to woodfibers at two to one by weight and a content of eight and a half percentof binder by weight, the building board may have a density of sixteenpounds per cubic foot with minute air spaces or voids accounting forclose to seventy five percent of the total mass or volume. However, alower content of wood fibers is preferred to minimize their blocking andlaminating effects.

The apparatus shown in FIGURE 2 is similar to that of FIGURE 1 exceptfor the arrangement whereby the tion of the wood fibers in the collectedpack is quite 6 satisfactory although not as thorough as with theapparatus of FIGURE 1.

While the building boards produced by the equipment of FIGURES 1 and 2possess the desired qualities, a rather excessive amount of binder isutilized since a large proportion of it is buried in the wood fibercomponent. The binder serves little purpose in connection with the woodfibers since they are inclined to mat or felt together, particularlywhen wet, and to attach themselves to the glass fibers without the aidof any cohesive agent. This waste of binder is greater than would beexpected in view of the bulk of the wood fibers, their specific gravitybeing around .4 and accordingly much lower than that of the glassfibers.

An arrangement permitting a substantial saving in the quantity of bindermaterial is illustrated in FIGURE 3. In this method a glass fiber packimpregnated with binder is formed in the normal manner in a glass woolforming line and is delivered by a conveyor 31 to the upperly inclinedconveyor 32. This angled conveyor 32 feeds the uncured, or partiallycured, pack into a reforming unit in which there is a main roller 34covered with projecting spikes 35. This roller revolves clockwise asviewed in FIGURE 3. Adjacent to the roller 34 are smaller rollers 36 and37 likewise'having spikes around their peripheral surfaces. The rollers36 and 37 turn in the opposite direction to that of roller 34 and theirspikes intermesh with the spikes of the large roller.

Through the cooperative action of these three rollers the pack offibrous glass is torn into clumps and tufts and discharged downwardlywithin hood 39. A cleaning roller 38 positioned below roller 34, alsorotating clockwise has spikes which remove glass fibers clinging to. thespikes of roller 34. If deired a supplemental quantity of binder may beintroduced into hood 39 through nozzle 49. The clumps and tufts of glassfibers are collected and reassembled into a pack on conveyor 43 with theassistance of air movement through the conveyor into suction chamber 45.This flow of air may be controlled by a damper in air inlet 46. Woodfibers are discharged into the hood 39 through piping 47 under the driveof a blower 48. The wood fibers are interspersed among the fallingclumps of fibrous glass and become a part of the reformed pack.

These wood fibers may be in the same wet state as those introduceddirectly into the glass forming hood or spouts of the apparatus shown inFIGURES 1 and 2. However, in order that the water carried by the woodfibers does not adversely afi ect the binder with which the glass fibersare impregnated by dilution, in case the binder has not been brought toan insoluble state, it is preferred that the wood fibers here introducedcarry a smaller amount of moisture. Also, the less water incorporatedwith the wood fibers, the more quickly and more completely may thecuring of v the pack be completed. Nevertheless, thewood fibers shouldbe wet enough to interfelt and to have felting action with adjacentglass fibers. This is particularly desirable where the woodfibercomponent is high and more of the ultimate strength of the boardmust be derived from this constituent.

The resulting pack 49 is delivered to a receiving conveyor 50 andcarried thereby under a compression upper flight 51. While compressed itis transported through a curing oven for complete setting of the bindercomponent and establishment of the pack in a permanently compacted form.

In FIGURE 4 a special curing oven is shown in which a stationary skidplate is utilized instead of an upper conveyor flight for compressingthe glass fiber and wood fiber pack. As illustrated, the pack 55 arrivesfrom the forming apparatus and is delivered to a conveyor 57 by which itis carried through the oven 58. A pro-compression roller 59 reduces thepack thickness and prepares it for entry beneath the skid plate 60. Thelatter is mounted upon .rods 61 and '62, the height of whichisadjustable through nuts 63.

High'temperatureah is deliveredto the'oven through inlet 65 'and pa'ssesthrough the perforated skid plate'int'o and through the pack. Thisheated air brings the resinous binder with which the pack is impregnatedto at least a semi-cured, set stage. After passing through the pack,theair is exhausted through outlet 67.

With-the binder cured to' the point Where it holds the glass and'woodfiber-mass to its compressed thickness, the final curing maybeaccomplished in a subsequent chamber 70 where the heated air has directaccess to the pack without'an'y intervening upper flight or skid plate.

The skid plate 60 is preferably formed with depressed edges 71-as'may'beseen in the cross section of FIGURE Through this design, theedges of the pack and or" the/building board whichis made therefrom arehighly condensed. They are thus stronger than the edges of a boardhaving the same'thickness throughout its area. These depressed edgesalso have the added advantage of providing water vapor escape passages,when the boards aremounted with the compacted edges in a; verticalposition, by which water vapor may reach venting openings in theouter'covering of the wall, whether of siding or of other surfacingmaterial.

A partial perspective view of a building board with condensededge'portions produced by the apparatus of FIG- URES 4 and 5 is shown inFIGURE 6. Bordering its main body section 73 are the strengthened edgestrips 74 and 75. By having downwardly ofiset shoulders on the'ends ofindividual cross panels of an upper conveyor compression flight, a boardmay be produced of'the skid formed'design illustrated'in FIGURE 6.

'By shaping thecompression conveyor cross-panels with angularlydirected'ridges, in'addition to shouldered ends, a board 77, asperspectively illustrated in FIGURE 7, may be produced with one or morecentered zigzag channels such as 78 and condensed edge strips 74 and 75.Such an angular channel improves the racking strength of the board bydiagonal bracing as well as furnishes another path'forexpanding watervapor. It also provides an' additional area of extra nail holdingcapacity. A conveyor panel of a single design may be utilized inassembling an upper compression flight for producing such boards byturning alternate panels endwise.

A portion of a wall incorporating aboard such as that illustrated'in'FIG-URE 7 is shown in perspective in'FIG- URE 8. Both a horizontaland vertical sectionof the Wall are included in this view. The interiorof the wall is faced with a gypsum board 81 set against two by fourstuds 82. Nailed to outside edges of the studs is a sheath.- ing board84 having compacted vertical edges 86 and a centered vertical channel87. The board is secured tothe studs by nails through the compactedsections. The exteriorsurface of'the wall comprises lapped siding 88nailed through the sheathing board to the studs.

Water vapor generated within the dwelling follows the paths indicated byarrows through the permeable gypsum board and across the airspacebetween the studs. It then travels'through'theporoussheathing-board to reach the vertical venting channels' providedin its exterior surface. If there are natural cracks between the sidingstrips the vapor readily passes to the outside atmosphere. In case thesiding is closely installed, small wedges 90 may be driven betweenadjacent siding strips along the top and bottom of the wall to providevapor exit openings. As mentioned earlier, this escape of the watervapor will occur even though the. outside temperature sufficiently lowtoestablish'a dew or saturation pointjwithin the sheathing board or thesiding.

ln-c'as'e accidental or purposelyarranged vapor exhaust outlets do-notexist, and the outside surfacing material constitutes a substantialvapor'barrier, there'will be condensation of water on the inner surfaceof the siding.

water will run into'the sheathing where it is held 7 by the absorbentwood fibers. However, because of the high porosity of this fibrous glassand wood board, and the dispersal of the wood fibers therethrou gh, themoisture will 'be quick to evaporate and diffuse'on a subsequent rise oftemperature. This is in marked contrast with the slow dissipation ofwater vapor from a closely packed all-organic fiber board. It shouldhere be again pointed out that the higher resistance of the organicboard caus'es the vaporto condense whether or not there is free passagefor the vapor beyond the exterior side of the board.

Because of the strong network of bonded fiberglass and thenon-continuous distribution of wood fibers, the building board of thisinvention is not weakened materially by the absorbed water and itsthermal insulating ca pacity is not seriously impaired. V

In addition 'to redwood and fir fibers specifically referred to herein,other wood and organic fibers are equally adaptable to this invention.Soft wood fibers in general, such as pine and spruce, would besatisfactory as would be bagasse, fibers prepared from sugar cane.

Although the description has been restricted to fibrous glass, thecoarser mineral fibers of rock and slag wood may be used as the mainconstituent, even though,- as is well known, their qualities are belowthose of standard glass fibers.

Also, while the building board of this invention is of prime value as awall or roof sheathing, its mertitable features are advantageous whenthe board is used for other purposes.

Should it be desired to increase the resistance of the board to themovement of water vapor, when there is an inadequate'outlet for vaporbeyond the board, a semi-pervious coating of gypsum may be applied tothe interior surfaceof the board. Through this extra resistance, theaction of the board will be similar to that of an all organic boardcausing precipitation of water therein in'advance of outer wallsurfacing material.

The proportion of, glass fibers to organic fibers may vary, inboards-coming within the province of this invention, throughout a widerange. Various considerations may afiect the determination of therelative amounts of the two types of fibers to include. 7

Should dimensional stability, long lasting immunity to weathering,superior insulating properties be of utmost concern, the glass fibercontent should be increased. If cost is important or in case a heavierbodied or more closely knit board is preferred, the organic fiber sharemay be made more dominant. In the first case the binding together of theglass fibers is relied upon for the primary strength of theboard withthe wood fibers spaced compartively sparsely therethroughr V In thelatter composition, the strength of the board is to a greater extentderived from the more continuous formation of intervening wood fibers. Alarger quantity of wood fibers may be better introduced where the mixingis accomplished in the glass fiber forming hood. Likewise, longer woodfibers are favored in the hood'mix'ing system. When the organic 'fibe'rsare added in a reform unit, a lower quantity and shorter fibers aredesirable in order 'that they-mo re easily penetrate the glass fiberclumps and do not form layers over the clumps.

Whatever ratio of constituents are utilized in following the precepts ofthis invention, the resulting building board.

From the foregoing it may be perceived that ample means and methods havebeen provided for realizing the objects of the invention. At the sametime it will be under stood that numerous changes may be made inmaterials and methods without departing from the spirit of thisinvention and the scope of the appended claims.

I claim:

1. A fibrous pack from which a building board is produced includingsubstantially dry glass fibers, dispersed particles of a heat settablebinder, said binder having a strong aflinity for the dry glass fibers,and coarse, unbeaten and unslurried, shredded wood fibers interspersedamong the glass fibers, said wood fibers being wet but carryinginsufficient water to materially wet the glass fibers.

2. A fibrous pack according to claim 1 in which most of the glass fibersare in loose binder-impregnated clumps and the wood fibers arebinder-free and are disposed generally exteriorly of the clumps.

3. A method of producing a fibrous building board which comprisescreating a web of glass fibers impregnated with an uncured binder,tearing the web into clumps and letting the clumps fall upon acollecting surface, interspersing coarse, wet wood fibers among theclumps of the web as they fall upon the collecting surface, said wetWood fibers being free of an excess of water, compressing the resultingmixed mass of glass fiber clumps and wood fibers and curing the binderwhile the mass is compressed.

4. A method of producing a fibrous building board which comprises mixingand massing comparatively dry 30 glass fibers, coarse, wet, wood fibersand -a binding agent, said wood fibers carrying an insufiicient quantityof water to materially wet the dry glass fibers, compressing theresulting mass of fibers, impregnated with the binding agent, andapplying heat While the mass is compressed to set the binding agent andsimultaneously drive the moisture from the wet wood fibers, theevaporation of the water from the wood fibers blocking the adhesion ofthe binding agent to the wood fibers.

5. A building board composed of evenly distributed bonded glass fibersand loosely incorporated coarse wood fibers and having a hardimpermeable binding agent, said binding agent being attached to theglass fibers and having a minimum attachment to the wood fibers, wherebythe surfaces of the wood fibers are largely uncoated with the bindingagent and hence are capable of readily absorbing moisture, theproportion by weight of the glass fibers to the wood fibers beingbetween one and six parts of the glass fibers to one part of the woodfibers.

References Cited in the file of this patent UNITED STATES PATENTS1,790,178 Sutherland Jan. 27, 1931 1,996,082 Powell Apr. 2, 19352,288,072 Collins June 30, 1942 2,639,759 Sirnison May 26, 19532,658,848 Labino Nov. 10, 1953 2,702,241 Hawley Feb. 15, 1955 2,772,603Waggoner Dec. 4, 1956

3. A METHOD OF PRODUCING A FIBROUS BUILDING BOARD WHICH COMPRISESCREATING A WEB OF GLASS FIBERS IMPREGNATED WITH AN UNCURED BINDER,TEARING THE WEB INTO CLUMPS AND LETTING THE CLUMPS FALL UPON ACOLLECTING SURFACE, INTERSPERSING COARSE, WET WOOD FIBERS AMONG THECLUMPS OF THE WEB AS THEY FALL UPON THE COLLECTING SURFACE, SAID WET